The so-called Building Administration Law (Law on Maintenance of Sanitation in Buildings) provides that indoor temperature be maintained at 17 [degrees C.] to 28 [degrees C.] and relative humidity be maintained at 40 [%] to 70 [%] as control standard values for the air environment in specific buildings such as commercial facilities and offices having floor areas of 3,000 [m2] or more. The indoor temperature is controlled relatively easily along with the growing use of air-conditioners (air-conditioning apparatus). However, it is hard to say that the relative humidity is controlled sufficiently. In particular, lack of the amount of humidification in winter is a challenge to address.
As related-art indoor humidification methods, evaporative, steam, and water spray methods are given as examples. Among those methods, the evaporative method is a method of causing air to pass through a filter having water absorption capability to exchange heat between water contained in the filter and an air current, thereby evaporating the water from the filter for indoor humidification. Further, the steam method is a method of an energizing heating unit for heating water inside a water reservoir, thereby evaporating water for indoor humidification. Still further, the water spray method is a method of atomizing water through pressurization to exchange heat between the atomized water and the air current, thereby performing indoor humidification.
As a related-art humidifier using the evaporative humidification method, there is proposed a humidifier constructed such that a plurality of rectangular strip-like humidification elements each formed of a sintered compact of hydrophilic polyethylene are inserted in line at an interval of 1 cm into a small box having a water tank (see, for example, Patent Literature 1).
Further, as another related art using the evaporative humidification method, there is disclosed an evaporative humidifier constructed such that a plurality of humidification elements each formed of a water absorbing material are arranged in an air passage, the ends of the humidification elements on one side are immersed into a water supply tank to absorb water, and the absorbed water is evaporated by the humidification elements, in which raised portions are formed on at least one surface of each of the humidification elements (see, for example, Patent Literature 2).
Further, as another related-art humidifier using the evaporative humidification method, there is proposed a humidifier constructed such that wet plates having water retention properties are arranged to face an air current (see, for example, Patent Literature 3).
Further, as another related art using the evaporative humidification method, there is proposed a humidification unit constructed such that water retaining members each partially having projecting portions formed thereon are arranged in a laminated form on a porous composite sheet made of fibers of polyethylene terephthalate or the like (see, for example, Patent Literature 4).